Re: [PATCH v7 05/13] ACPI/PPTT: Add Processor Properties Topology Table parsing

[Ard Biesheuvel]

On 28 February 2018 at 22:06, Jeremy Linton <jeremy.linton@xxxxxxx> wrote:
> ACPI 6.2 adds a new table, which describes how processing units
> are related to each other in tree like fashion. Caches are
> also sprinkled throughout the tree and describe the properties
> of the caches in relation to other caches and processing units.
>
> Add the code to parse the cache hierarchy and report the total
> number of levels of cache for a given core using
> acpi_find_last_cache_level() as well as fill out the individual
> cores cache information with cache_setup_acpi() once the
> cpu_cacheinfo structure has been populated by the arch specific
> code.
>
> An additional patch later in the set adds the ability to report
> peers in the topology using find_acpi_cpu_topology()
> to report a unique ID for each processing unit at a given level
> in the tree. These unique id's can then be used to match related
> processing units which exist as threads, COD (clusters
> on die), within a given package, etc.
>
> Signed-off-by: Jeremy Linton <jeremy.linton@xxxxxxx>
> ---
>  drivers/acpi/pptt.c | 488 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 488 insertions(+)
>  create mode 100644 drivers/acpi/pptt.c
>
> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
> new file mode 100644
> index 000000000000..883e4318c6cd
> --- /dev/null
> +++ b/drivers/acpi/pptt.c
...
> +/* total number of attributes checked by the properties code */
> +#define PPTT_CHECKED_ATTRIBUTES 4
> +
> +/*
> + * The ACPI spec implies that the fields in the cache structures are used to
> + * extend and correct the information probed from the hardware. Lets only
> + * set fields that we determine are VALID.
> + */
> +static void update_cache_properties(struct cacheinfo *this_leaf,
> +                                   struct acpi_pptt_cache *found_cache,
> +                                   struct acpi_pptt_processor *cpu_node)
> +{
> +       int valid_flags = 0;
> +
> +       if (found_cache->flags & ACPI_PPTT_SIZE_PROPERTY_VALID) {
> +               this_leaf->size = found_cache->size;
> +               valid_flags++;
> +       }
> +       if (found_cache->flags & ACPI_PPTT_LINE_SIZE_VALID) {
> +               this_leaf->coherency_line_size = found_cache->line_size;
> +               valid_flags++;
> +       }
> +       if (found_cache->flags & ACPI_PPTT_NUMBER_OF_SETS_VALID) {
> +               this_leaf->number_of_sets = found_cache->number_of_sets;
> +               valid_flags++;
> +       }
> +       if (found_cache->flags & ACPI_PPTT_ASSOCIATIVITY_VALID) {
> +               this_leaf->ways_of_associativity = found_cache->associativity;
> +               valid_flags++;
> +       }
> +       if (found_cache->flags & ACPI_PPTT_WRITE_POLICY_VALID) {
> +               switch (found_cache->attributes & ACPI_PPTT_MASK_WRITE_POLICY) {
> +               case ACPI_PPTT_CACHE_POLICY_WT:
> +                       this_leaf->attributes = CACHE_WRITE_THROUGH;
> +                       break;
> +               case ACPI_PPTT_CACHE_POLICY_WB:
> +                       this_leaf->attributes = CACHE_WRITE_BACK;
> +                       break;
> +               }
> +       }
> +       if (found_cache->flags & ACPI_PPTT_ALLOCATION_TYPE_VALID) {
> +               switch (found_cache->attributes & ACPI_PPTT_MASK_ALLOCATION_TYPE) {
> +               case ACPI_PPTT_CACHE_READ_ALLOCATE:
> +                       this_leaf->attributes |= CACHE_READ_ALLOCATE;
> +                       break;
> +               case ACPI_PPTT_CACHE_WRITE_ALLOCATE:
> +                       this_leaf->attributes |= CACHE_WRITE_ALLOCATE;
> +                       break;
> +               case ACPI_PPTT_CACHE_RW_ALLOCATE:
> +               case ACPI_PPTT_CACHE_RW_ALLOCATE_ALT:
> +                       this_leaf->attributes |=
> +                               CACHE_READ_ALLOCATE | CACHE_WRITE_ALLOCATE;
> +                       break;
> +               }
> +       }
> +       /*
> +        * If the above flags are valid, and the cache type is NOCACHE
> +        * update the cache type as well.
> +        */
> +       if ((this_leaf->type == CACHE_TYPE_NOCACHE) &&
> +           (valid_flags == PPTT_CHECKED_ATTRIBUTES))
> +               this_leaf->type = CACHE_TYPE_UNIFIED;

Why do we need the associativity and #sets attributes to be valid in
order to set the cache type?

I see how size and line size are rather fundamental properties, but
for a system cache, the geometry doesn't really matter.

> +}
> +
> +/*
> + * Update the kernel cache information for each level of cache
> + * associated with the given acpi cpu.
> + */
> +static void cache_setup_acpi_cpu(struct acpi_table_header *table,
> +                                unsigned int cpu)
> +{
> +       struct acpi_pptt_cache *found_cache;
> +       struct cpu_cacheinfo *this_cpu_ci = get_cpu_cacheinfo(cpu);
> +       u32 acpi_cpu_id = get_acpi_id_for_cpu(cpu);
> +       struct cacheinfo *this_leaf;
> +       unsigned int index = 0;
> +       struct acpi_pptt_processor *cpu_node = NULL;
> +
> +       while (index < get_cpu_cacheinfo(cpu)->num_leaves) {
> +               this_leaf = this_cpu_ci->info_list + index;
> +               found_cache = acpi_find_cache_node(table, acpi_cpu_id,
> +                                                  this_leaf->type,
> +                                                  this_leaf->level,
> +                                                  &cpu_node);
> +               pr_debug("found = %p %p\n", found_cache, cpu_node);
> +               if (found_cache)
> +                       update_cache_properties(this_leaf,
> +                                               found_cache,
> +                                               cpu_node);
> +
> +               index++;
> +       }
> +}
> +
> +/**
> + * acpi_find_last_cache_level() - Determines the number of cache levels for a PE
> + * @cpu: Kernel logical cpu number
> + *
> + * Given a logical cpu number, returns the number of levels of cache represented
> + * in the PPTT. Errors caused by lack of a PPTT table, or otherwise, return 0
> + * indicating we didn't find any cache levels.
> + *
> + * Return: Cache levels visible to this core.
> + */
> +int acpi_find_last_cache_level(unsigned int cpu)
> +{
> +       u32 acpi_cpu_id;
> +       struct acpi_table_header *table;
> +       int number_of_levels = 0;
> +       acpi_status status;
> +
> +       pr_debug("Cache Setup find last level cpu=%d\n", cpu);
> +
> +       acpi_cpu_id = get_acpi_id_for_cpu(cpu);
> +       status = acpi_get_table(ACPI_SIG_PPTT, 0, &table);
> +       if (ACPI_FAILURE(status)) {
> +               pr_err_once("No PPTT table found, cache topology may be inaccurate\n");
> +       } else {
> +               number_of_levels = acpi_find_cache_levels(table, acpi_cpu_id);
> +               acpi_put_table(table);
> +       }
> +       pr_debug("Cache Setup find last level level=%d\n", number_of_levels);
> +
> +       return number_of_levels;
> +}
> +
> +/**
> + * cache_setup_acpi() - Override CPU cache topology with data from the PPTT
> + * @cpu: Kernel logical cpu number
> + *
> + * Updates the global cache info provided by cpu_get_cacheinfo()
> + * when there are valid properties in the acpi_pptt_cache nodes. A
> + * successful parse may not result in any updates if none of the
> + * cache levels have any valid flags set.  Futher, a unique value is
> + * associated with each known CPU cache entry. This unique value
> + * can be used to determine whether caches are shared between cpus.
> + *
> + * Return: -ENOENT on failure to find table, or 0 on success
> + */
> +int cache_setup_acpi(unsigned int cpu)
> +{
> +       struct acpi_table_header *table;
> +       acpi_status status;
> +
> +       pr_debug("Cache Setup ACPI cpu %d\n", cpu);
> +
> +       status = acpi_get_table(ACPI_SIG_PPTT, 0, &table);
> +       if (ACPI_FAILURE(status)) {
> +               pr_err_once("No PPTT table found, cache topology may be inaccurate\n");
> +               return -ENOENT;
> +       }
> +
> +       cache_setup_acpi_cpu(table, cpu);
> +       acpi_put_table(table);
> +
> +       return status;
> +}
> --
> 2.13.6
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel